The invention relates to magnetic devices such as inductors and transformers. Specifically, the invention relates to magnetic devices that can be assembled as low profile surface mount devices on a printed circuit board or a metallized substrate.
Magnetic devices, such as inductors and transformers, are employed in many different types of electrical devices including communications equipment and power supplies. In practice, most magnetic devices are fabricated of one or more windings, formed by an elongated electrical conductor, such as a wire of circular or rectangular cross-section, or a planar electrical conductor wound about or mounted to a bobbin composed of a dielectric material, such as plastic. In some instances, the electrical member is soldered to terminations on the bobbin. Alternatively, the electrical member may be threaded through the bobbin for connection directly to a metallized area of an underlying circuit board. A magnetic core may be disposed about the bobbin to impart a greater reactance to the magnetic device and thereby alter its operating characteristics. The use of a bobbin, however, generally results in a magnetic device with a large profile, which not only takes up valuable space on the circuit board, but also results in a large height for the overall electrical device.
In addition to being formed with bobbins, magnetic devices can be formed with a magnetic core, such as ferrite or iron, wound with conductive coils. These devices are sometimes referred to as wire-wound core devices. One major difficulty with wire-wound core devices is that they have been difficult to miniaturize. While components such as resistors, diodes, capacitors and transistors have been drastically reduced in size, magnetics, including bobbin and wire-wound core devices, remain bulky.
One attempt at a low profile magnetic device is described in U.S. Pat. No. 5,574,420 issued Nov. 12, 1996 to Roy et al. The device described in Roy et al. is a magnetic component formed by a plurality of conductive elements surrounding a magnetic core. The conductive elements pass through holes or channels in the magnetic core and then are bent outwards to allow surface mount connection to a printed wiring board or the equivalent. Unfortunately, the magnetic component described by Roy et al. suffers from a number of deficiencies. First, the device is incapable of carrying large amounts of current because the small area of the magnetic core that is surrounded by the conductive elements tends to saturate quickly. Second, the bent out ends of the conductive elements make poor surface mount conductors because they are very difficult to make coplanar. Finally, the magnetic components of Roy et al. can be difficult to manufacture due to the shape of the magnetic core and the arrangement of the conductive elements.
Accordingly, what is needed is a low profile magnetic component that is capable of handling larger currents, has more consistently coplanar conductor elements, and is more easily manufactured.
Embodiments of the invention include providing for a low profile magnetic component formed from a magnetic core and a plurality of conductive elements, also referred to as conductors. The magnetic core includes a bottom, a top, end surfaces and side surfaces. The side surfaces include portions that are angled inward from the bottom to the top thereby forming a plurality of channels. The magnetic core further includes a recess in the top adjacent to the channels.
The plurality of conductors surround the magnetic core and pass through a corresponding channel from the plurality of channels. The top of the conductors are adjacent to the recess in the magnetic core and the ends are bent inward against the bottom of the core. The ends of the conductors form contact surfaces which are coplanar and surface mountable. In order to form the conductors tightly around the magnetic core and to ensure that the contact surfaces formed by the ends are coplanar, during manufacture the tops of the conductors are loaded causing the ends to bend inward in to the recess in the magnetic core. While the conductors are loaded the ends are bent inward toward the center of the bottom. After bending, the conductors are unloaded and the spring tension in the conductors causes them to fit tightly around the magnetic core and causes the ends to fit snugly against the base.
The magnetic components can be formed into a magnetic device such as an inductor by placing two or more in close proximity and using conductive traces on a printed wiring board or other insulated substrate to form the conductors into windings. This magnetic device can then be utilized in a power supply as, for example, the inductor in an output filter or as transformers in groups of two or more.
The foregoing has outlined, rather broadly, preferred and alternative features of embodiments of the invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art will appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the invention. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.